The present invention relates to a method and apparatus for damping the steering movement, especially of a motorcycle, with a steering damper adjustable in its damping value.
During driving operation of a motorcycle, interferences of the stabilization occur over the entire speed range. On the one hand, a steering flutter is noticeable, for example, at a speed below 100 km/h. At higher velocity, for example, up to 150 km/h, a steering chatter occurs which is caused in particular by road shocks and impacts. At still higher velocities, a so-called high velocity swinging or hunting may finally occur.
In order to reduce or eliminate the two first-mentioned interferences, steering dampers have proved to be of value. For example, the DE-AS No. 23 38 720 shows such a steering damper whose damping value can be adjusted by hand. The once-adjusted damping value remains constant over the entire angular range of the steering deflection.
On the other hand, a steering damper may be counterproductive if the vehicle is moved in city traffic at low velocities and large steering deflections become necessary in that case for purposes of evasive maneuvers. An effective steering damper impairs in this case the handling ability of the motorcycle.
Furthermore, motorcycles with an effective steering damper tend more to high velocity swinging or hunting than those motorcycles without steering damper. It should be mentioned in connection therewith that at high velocities the steering movements of the motorcycle no longer take place by way of steering deflections but by inclining of the vehicle with the driver. The steering therefore remains nearly in the zero position during high velocity hunting or swinging.
It is the object of the present invention to provide a method and apparatus for damping steering movements of the aforementioned type in which the steering damper remains ineffectual in city traffic, also at very high velocities but in contrast becomes effective in velocity ranges in which steering chatter and steering flutter occur.
The underlying problems are solved according to the present invention in that measured values concerning the steering angle and the driving velocity are fed continuously to an electronic evaluating circuit, the evaluating circuit continuously compares the measured values with predetermined constant threshold values and when both measured values exceed their respective threshold value, the evaluation circuit produces a signal for changing the damping value of the steering damper.
According to the present invention, the driving velocity and the steering angle are therefore continuously measured. If they exceed an adjusted threshold value, then the steering damper is activated and is changed in its damping value. The steering damper may thereby involve any commercially available steering damper. It may be constructed on a hydraulic basis; however, magnetic friction dampers can also be used.
It is important according to the present invention that both measured values must have exceeded their threshold value in order to effect a change of the damping value. For only at higher velocities than at the adjusted threshold value and at the correspondingly higher steering angle either a steering wheel chatter or steering wheel flutter will occur.
If the motorcycle drives at very high velocity and if the steering angle deflection remains below the predetermined threshold value, then a high velocity swinging or hunting may nonetheless occur. A permanently effective steering damper, as already mentioned, would be harmful in that case.
Analogously, at low velocities, the steering damper should not to become effective, i.e., the steering will therefore be easy to handle for evasive maneuvers, also when the steering angle exceeds its threshold value.
As already pointed out, the steering chatter stems from road shocks and road impacts. In another embodiment of the present invention the telescoping acceleration of the telescopic fork is measured for the elimination of the steering chatter. If the telescoping acceleration exceeds an adjusted threshold value, which means that the front wheel drives over a road unevenness, then also in this case the steering damper is activated in the direction of a higher damping value. This measure is used in conjunction with the measurement of the driving velocity. However, in this case, only the steering chatter is suppressed. It is more appropriate in many cases to combine the same with the measurement of the steering deflection angle in order thus to combat also the steering flutter.
As a rule, the vehicle is moved in city traffic in a speed range up to 50 km/h. It is therefore meaningful to place the threshold value of the driving velocity within a range between 40 to 60 km/h. It has also been found that the steering deflections at the high velocity hunting lie below +0.5.degree.. Analogously, the threshold value is therefore to he adjusted in an advantageous embodiment at 0.3.degree. to 0.7.degree..
With certain types of motorcycles, very high damping values are required for controlling the steering chatter. However, such high damping values prevent a restoring or return of the steering system to straight drive. In a further advantageous realization of the present invention, the damping value therefore rises to very high values in case of activation over-proportionally to the deflection angle. After reaching the maximum deflection angle, the electronic evaluation circuit immediately takes the steering damper back to a lower or to the original damping value. This can be achieved in that in addition to the steering angle, also the steering angle velocity of the steering movement is measured. If it approaches zero with a steering angle above the threshold value, this is an indication that the steering deflection has reached its maximum value. If the evaluation circuit receives in this case an angle velocity of zero or nearly zero with a gradient toward zero, then it switches the steering damper to ineffective and the driver can move the steering control handle back into straight driving position.
If acceptable damping forces are sufficient during steering chatters, then this measure can be dispensed with. However, the damping value is then taken back by way of the electronic evaluation circuit to its original value after a lapse of a certain time interval, preferably three seconds.
The method and apparatus according to the present invention are suited in a particularly favorable manner for motorcycles. However, it is not limited thereto. It is also apparent that it can be used with other types of vehicles having steering mechanisms.